The operation of computers and other electronic equipment is accompanied by unwanted electromagnetic interference (known simply as `noise` by electrical engineers). Electromagnetic interference (EMI) generated from a given device can be communicated back to that device. Moreover, the radiation emitted from one or more separate but adjacent devices can combine synergistically to create still more noise. As the number of electronic parts in an automobile increases so does the amount of electromagnetic interference (EMI) ambient in the automobile.
Further, the tendency to make electronic equipment smaller causes an increase in the density of radiation-emitting devices and the proximity of such devices to one another, thereby augmenting the effects of EMI on surrounding circuitry. Additionally, the recent exponential increase in the number of wireless communications devices increases the amount of ambient EMI in modem autos.
These pressures underscore the importance of EMI suppression in electronic designs in an auto. The issue is all the more important in the dashboard of a modern automobile where numerous electrical and electronic components are located in confined quarters and, usually, near an automobile engine. For the automobile passengers, the issue is poignant because it can affect the performance of audio equipment they listen to while driving.
Another problem in the design of electronic modules is maintaining the stability of oscillator frequency of the electronic module. Prior dashboard light circuits control current to auto dashboard dimmer lights using a rheostat, but the heat generated by the rheostat is substantial and limits the life of the dashboard light as well as heat-sensitive plastics in and around the dashboard. In more recent dashboard dimmer light circuits, a pulse-width-modulated (PWM) signal limits the on-time of a dashboard dimmer light to reduce the average power consumption of the dashboard dimmer light in proportion to the duty cycle of the PWM signal. These designs vary the duty cycle through a step-wise bank of discrete resistors, they affect the frequency of the PWM signal. This, in turn, can affect the EMI and therefore the radio, cell phone, etc.